thumbnail

Geology, Ground-Water Occurrence, and Estimated Well Yields from the Mariana Limestone, Kagman Area, Saipan, Commonwealth of the Northern Mariana Islands

Water-Resources Investigations Report 98-4077
By: , , and 
https://doi.org/10.3133/wri984077

Links

Abstract

A study of the geology, ground-water occurrence, and estimated well yields from the Mariana Limestone was done to investigate ground-water availability in the Kagman area, Saipan. The Mariana and Tagpochau Limestone formations form the major aquifer in the Kagman drainage basin. The Mariana Limestone, which is the major water-bearing unit in the Kagman area, ranges in thickness from 300 to 500 feet and contains intermittent, thin clay stringers. The calcareous rocks of the Tagpochau Limestone range in thickness from 500 to 1,000 feet and are more sandy than those of the Mariana Limestone. Ground water is unconfined in the Mariana Limestone and ranges from unconfined to confined in the Tagpochau Limestone. The fresh ground-water lens (that part of the lens with less than 2-percent of the chloride-ion concentration in seawater) in the Mariana Limestone is relatively thin, ranging from about 15 to 21 feet. Altitude of the water table ranges from about 1.5 to 2.5 feet above mean sea level. Freshwater in the Mariana Limestone is underlain by seawater and is separated by a transition zone about 8 to 25 feet thick. Hydraulic conductivity and transmissivity of the Mariana Limestone were calculated from data collected at six test wells. Using the Newman method, estimated hydraulic conductivity and transmissivity range from 290 to 2,500 feet per day and 7,600 to 62,000 feet squared per day, respectively. The higher values probably are indicative of average conditions in the Mariana Limestone. The estimated storage coefficient of the Mariana Limestone is about 0.1. The availability of water from the Mariana Limestone is restricted by the thinness of the freshwater lens. Results of the study indicate that fresh ground water can be obtained from the Mariana Limestone when wells are designed for minimum drawdown, effectively skimming freshwater from the top of the lens. Wells that are shallow, widely spaced, and pumped at low uniform rates can prevent saltwater intrusion. Calculated long-term yields of wells are about 30 gallons per minute or less for potable water.

Suggested Citation

Hoffmann, J.P., Carruth, R., Meyer, W., 1998, Geology, Ground-Water Occurrence, and Estimated Well Yields from the Mariana Limestone, Kagman Area, Saipan, Commonwealth of the Northern Mariana Islands: U.S. Geological Survey Water-Resources Investigations Report 98-4077, iv, 38 p., https://doi.org/10.3133/wri984077.

Publication type Report
Publication Subtype USGS Numbered Series
Title Geology, Ground-Water Occurrence, and Estimated Well Yields from the Mariana Limestone, Kagman Area, Saipan, Commonwealth of the Northern Mariana Islands
Series title Water-Resources Investigations Report
Series number 98-4077
DOI 10.3133/wri984077
Year Published 1998
Language ENGLISH
Publisher Geological Survey (U.S.)
Contributing office(s) Pacific Islands Water Science Center
Description iv, 38 p.
Additional publication details